Moisture adsorbing and desorbing material

ABSTRACT

An object of the present invention is to provide a water adsorbing/desorbing organic polymer material having excellent water adsorbing/desorbing performance and which is inexpensive and readily disposable by incineration or the like. In order to attain this object, water adsorbing/desorbing organic polymer materials of the present invention are characterized by having a polymer side chain containing a hydrophilic group on the backbone of an organic polymer base.

FIELD OF THE INVENTION

The present invention relates to materials adsorbing/desorbing water ingases. Particularly, the present invention relates to desiccants usedfor controlling the humidity in air-conditioners.

PRIOR ART

Desiccant air-conditioners incorporating an equipment capable ofcontinuously adsorbing/desorbing water with a desiccant have beencommercialized.

Performance of such desiccant air-conditioners greatly depends on theperformance of the desiccant used therein. Conventional desiccants forthis purpose were inorganic desiccants such as silica gel and zeolite.Such desiccants are used to adsorb water at room temperature, and afterthey are used for a period, they should desorb water by passing hightemperature air therethrough to regenerate adsorption performance. Theabove inorganic materials could attain a reasonable performance in awide temperature range from 20° C. for water adsorption to 100° C. forwater desorption because they are heat-resistant enough to endure airflow at a high temperature of 100° C. or more fed to desiccants.

However, further improvement in performance of desiccants is requiredfrom the social background of resource saving, energy saving and globalenvironmental protection. Namely, there is an urgent need for measuresagainst the heating temperature of the regenerating air, the heatcapacity of desiccants, formability, selection of readily disposablematerials, etc.

As one of measures, the use of organic polymer materials having a wateradsorbing/desorbing function has been proposed and suggested to becapable of lowering the heating temperature of the regenerating air.Representative examples of such organic polymer materials having a wateradsorbing/desorbing function are ion exchange resins.

Water adsorbing/desorbing performance of organic polymer materialsgreatly depends on the nature of the functional group (hydrophilicgroup) and the polymer structure. Hydrophilic groups can adsorb water bycoordinating water around them, but sufficient water adsorbing/desorbingperformance cannot be expected unless organic polymers have a polymerstructure in which water molecules can readily diffuse aroundhydrophilic groups.

In all desiccants comprising organic polymer materials so far proposedincluding ion exchange resins, the polymer chain has a crosslinkedstructure, which blocks diffusion of water molecules so that thesedesiccants could not attain sufficient water adsorbing/desorbingperformance though they have a hydrophilic group, whereby they had to becharged in considerable amounts in desiccant air-conditioners orinvolved high costs.

DISCLOSURE OF THE INVENTION

The present invention solves the problems of desiccants comprisingconventional organic polymer materials as described above and provides awater adsorbing/desorbing organic polymer material having excellentwater adsorbing/desorbing performance.

The present invention relates to a water adsorbing/desorbing materialcharacterized by having a polymer side chain containing a hydrophilicgroup on the backbone of an organic polymer base.

Generally, water adsorbing/desorbing materials comprising an organicpolymer contain a hydrophilic group on their polymer backbones to confera water adsorbing/desorbing function and the polymer backbones arecrosslinked to each other to compensate for deterioration of physicalstrength due to introduction of this hydrophilic group. Typical examplesthereof are ion exchange resins, in which an ion exchange group such asa sulfone or quaternary ammonium group has been generally introducedinto the backbone of a polystyrene obtained by polymerizing a styrenemonomer. However, these ion exchange groups become bulky by coordinatingseveral water molecules around them once they adsorb water, so that theresins are insufficient in physical strength and dissolve even in water.In order to solve this problem with ion exchange resins, polystyrenebackbones are crosslinked to each other with a crosslinker such asdivinylbenzene. This enhances physical strength of the resins, which nomore dissolve in water at the expense of lowered absorption/desorptionfunctions such as absorption speed or diffusion speed due to theformation of a crosslinked structure.

According to the present invention, it was found that excellent wateradsorbing/desorbing performance can be conferred on an organic polymerbase while keeping physical strength of the polymer backbone byintroducing a side chain in the form of a polymer chain containing ahydrophilic group onto the polymer backbone of the base. Wateradsorbing/desorbing materials of the present invention can considerablykeep adsorption/desorption speed and diffusion speed because theirpolymer backbones have no more crosslinked structure. In wateradsorbing/desorbing materials of the present invention, their polymerbackbones have the role of keeping physical strength or shape.

THE MOST PREFERRED EMBODIMENTS OF THE INVENTION

In water adsorbing/desorbing organic polymer materials of the presentinvention, suitable means for introducing a side chain in the form of apolymer chain containing a hydrophilic group onto the polymer backboneinclude graft polymerization. Especially, radiation-induced graftpolymerization is most preferred for the purpose of the presentinvention, because a desired graft polymer side chain can be introducedinto an organic polymer base by irradiating the base to produce aradical and reacting it with a graft monomer and the number or length ofthe graft chain can be relatively freely controlled and the polymer sidechain can be introduced into existing polymer materials in variousshapes.

In the present invention, materials that can be used as bases into whichis introduced a side chain in the form of a polymer chain containing ahydrophilic group include elemental polymer fibers and woven andnonwoven fabrics comprising an assembly thereof. Woven/nonwoven fabricmaterials can be suitably used as bases for radiation-induced graftpolymerization and they have a large surface area and are light and easyto process. Water adsorbing/desorbing materials prepared fromwoven/nonwoven fabrics can be easily handled during disposal and readilyincinerated, in contrast to conventional ion exchange resins having acrosslinked structure that are hard to incinerate.

Radiations that can be used in radiation-induced graft polymerizationwell suitable for the purpose of the present invention include α-rays,β-rays, γ-rays, electron rays, UV ray, etc., among which γ-rays andelectron rays are preferred for use in the present invention.Radiation-induced graft polymerization includes preirradiation graftpolymerization involving preliminarily irradiating a graft base and thenbringing it into contact with a polymerizable monomer (graft monomer)for reaction, and simultaneous irradiation graft polymerizationinvolving irradiating a system containing a base and a monomer, andeither method can be used in the present invention. Radiation-inducedgraft polymerization includes various manners of contact between amonomer and a base, such as liquid phase graft polymerization performedwith a base immersed in a monomer solution, gas phase graftpolymerization performed with a base in contact with the vapor of amonomer, or immersion gas phase graft polymerization performed byimmersing a base in a monomer solution and then removing it from themonomer solution for reaction in a gas phase, and any method can be usedin the present invention.

Fibers and woven/nonwoven fabrics comprising a fiber assembly are themost preferred materials for use as organic polymer bases for wateradsorbing/desorbing materials of the present invention, and are wellsuitable for use in the immersion gas phase graft polymerization becausethey tend to retain monomer solutions.

The hydrophilic group as a functional group for adsorbing/desorbingwater in water adsorbing/desorbing organic polymer materials of thepresent invention can be selected from ion exchange groups such ascation exchange groups and anion exchange groups and non-ion exchangegroups. Among them, ion exchange groups are preferred for the presentinvention because polymer graft side chains having an ion exchange groupthereon tend to expand by repulsive force due to charges of adjacent ionexchange groups and promote diffusion of water molecules. For example,sulfonate acid group is negatively charged so that graft side chainsrepulse each other to rise under the influence of adjacent sulfonateacid groups, thus increasing the mobility of the graft side chains.Conversely, quaternary ammonium group is positively charged so thatgraft side chains repulse each other to rise similarly under theinfluence of adjacent quaternary ammonium groups.

These polymer side chains containing a hydrophilic group can beintroduced onto the backbone of an organic polymer material bygraft-polymerizing a polymerizable monomer having a hydrophilic grouponto the backbone or by graft-polymerizing a polymerizable monomer nothaving a hydrophilic group by itself but capable of introducing ahydrophilic group onto the backbone and then introducing a hydrophilicgroup onto the grafted polymer side chain.

Among ion exchange groups, typical cation exchange groups are sulfonateacid group, phosphate group and carboxyl group, any of which can be usedas a hydrophilic group in water adsorbing/desorbing organic polymermaterials of the present invention. However, carboxyl group —COOH is notdissociated and graft side chains are interlaced by hydrogen bondsbetween carboxyl groups. This can be avoided by converting —COOH into analkali salt or alkali earth salt form (—COOMe). The problem associatedwith carboxyl group does not occur in ion exchange groups such assulfonate acid groups and phosphate groups because they are dissociatedwhether or not they are regenerative, but a global consideration isneeded to select their salt forms because those salt forms havedifferent water adsorbing/desorbing performance and heat stability.

Polymerizable monomers having a sulfonate acid group include sodiumstyrenesulfonate, sodium vinylsulfonate, sodium methallylsulfonate, etc.Polymerizable monomers having a carboxyl group include acrylic acid,methacrylic acid, etc. Sodium styrenesulfonate and acrylic acid can beused in combination to introduce a plurality of cation exchange groupsat the same time. Polymerizable monomers not having a cation exchangegroup by themselves but capable of introducing a cation exchange groupinclude glycidyl methacrylate, styrene, acrylonitrile, acrolein,chloromethylstyrene, etc. After these polymerizable monomers have beengraft-polymerized, a cation exchange group can be introduced by knownmethods. For example, a sulfonate acid group can be Introduced onto apolymer side chain by graft-polymerizing styrene on a base and thenreacting the grafted side chain with sulfuric acid or chlorosulfonicacid to sulfonate it.

These cation exchange groups introduced onto the polymer side chain canbe expected to not only adsorb water but also adsorb basic gases andremove positively charged particles.

Anion exchange groups that can be used as hydrophilic groups in wateradsorbing/desorbing organic polymer materials of the present inventioncan be selected from quaternary ammonium group, tertiary amino group,secondary amino group and primary amino group. However, quaternaryammonium group has limited applications because of the insufficient heatstability and emission of amine odor.

Polymerizable monomers having an anion exchange group includevinylbenzyltrimethylammonium chloride (VBTAC), dimethylaminoethylmethacrylate (DMAEMA), diethylaminoethyl methacrylate (DEAEMA),dimethylaminopropyl acrylamide (DKAPAA), etc. Polymerizable monomers nothaving an anion exchange group by themselves but capable of introducingan anion exchange group include glycidyl methacrylate, styrene,acrylonitrile, acrolein, chloromethylstyrene, etc. After thesepolymerizable monomers have been graft-polymerized, an anion exchangegroup can be introduced by known methods. For example, a quaternaryammonium group can be introduced onto a polymer side chain bygraft-polymerizing chloromethyletyrene on a base and then immersing thebase in an aqueous trimethylamine solution for conversion into aquaternary ammonium group.

These anion exchange groups introduced onto the polymer side chain canbe expected to not only adsorb water but also adsorb basic gases andremove negatively charged particles.

Non-ion exchangeable hydrophilic groups such as amide and hydroxylgroups can also be used as hydrophilic groups in wateradsorbing/desorbing organic polymer materials of the present invention.Polymerizable monomers having an amide group include acrylamide,dimethyl acrylamide, methacrylamide and isopropyl acrylamide, etc.Polymerizable monomers having a hydroxyl group include 2-hydroxyethylmethacrylate, etc. Polymerizable monomers not having these hydrophilicgroups by themselves but capable of introducing these hydrophilic groupsinclude glycidyl methacrylate, chloromethylstyrene, vinyl acetate, etc.After these polymerizable monomers have been graft-polymerized, ahydrophilic group can be introduced by known methods. For example, ahydroxyl group can be introduced onto a polymer side chain bygraft-polymerizing glycidyl methacrylate on a base and then treating thebase with an aqueous sulfuric acid solution with warming to open theepoxy group into a diol group.

A plurality of different kinds of hydrophilic groups can be introducedonto a graft side chain. For example, vinylbenzyltrimethylammoniumchloride (VBTAC) having a quaternary ammonium group is often used incombination with acrylamide-based hydrophilic monomers or ester-basedhydrophilic monomers because it is difficult to subject toradiation-induced graft polymerization alone, in which case a non-ionexchange group such as amide or ester group is introduced with the anionexchange quaternary ammonium group. Organic polymer materials having aplurality of different kinds of hydrophilic groups introduced onto theirgraft side chains can also be used as water adsorbing/desorbingmaterials of the present invention.

Organic polymer bases for water adsorbing/desorbing materials of thepresent invention are preferably polyolefin-based organic polymermaterials. Polyolefin-based organic polymer materials are suitable forthe purpose of introducing a graft side chain by radiation-induced graftpolymerization because they are not degradable by radiations.

Various embodiments of the present invention are explained below.However, the present invention is not limited to the followingdescription.

EXAMPLE 1

A heat-fused nonwoven cloth having an areal density of 50 g/m² made of apolyethylene terephthalate (core)/polyethylene (sheath) composite fiberof about 15 μm in diameter was used as an organic polymer base. Thisnonwoven cloth base was irradiated with γ-rays at 150 kGy in a nitrogenatmosphere and then immersed in glycidyl methacrylate and reacted at 50°C. for 4 hours to give a glycidyl methacrylate-grafted nonwoven cloth ata grafting degree of 133%. This grafted nonwoven cloth was immersed inan aqueous solution of 8% aqueous sodium sulfite and 12% isopropylalcohol and heated at 80° C. for 8 hours to give a strongly acid cationexchange nonwoven material having a neutral salt decomposition capacityof 2.81 meq/g.

The resulting nonwoven cloth was cut into 10 cm square and regeneratedwith hydrochloric acid and then dried in a dryer at 60° C. for 3 hours.The nonwoven cloth was removed from the dryer and placed on a bench in aroom at a relative humidity of 70% and a temperature of 25° C. where itwas tested for change with time in weight gain resulting from adsorptionof water in the air. A high water adsorption speed was obtained as shownby weight gains of 70 after 3 minutes and 12% after 10 minutes.

EXAMPLE 2

A nonwoven cloth base as used in Example 1 was Irradiated in the samemanner as described in Example 1 and then immersed in achloromethylstyrene solution and reacted at 40° C. for 7 hours tograft-polymerize chloromethylstyrene at a grafting degree of 116%. Thisnonwoven cloth was immersed in a 10% aqueous trimethylamine solution andreacted at 50° C. for 3 hours to give a strongly basic anion exchangenonwoven material having a neutral salt decomposition capacity of 2.32meq/g.

The resulting nonwoven cloth was cut into 10 cm square and regeneratedwith an aqueous sodium hydroxide solution and then dried in a dryer at50° C. for 5 hours. The nonwoven cloth was removed from the dryer andplaced on a bench in a room at a relative humidity of 55% and atemperature of 22° C. where it was tested for change with 5 time inweight gain resulting from adsorption of water in the air. A high wateradsorption speed was obtained as shown by weight gains of 5.8% after 3minutes and 10.3% after 10 minutes.

EXAMPLE 3

A nonwoven cloth base as used in Example 1 was Irradiated in the samemanner and then immersed in a nonionic hydrophilic monomer acrylamideand reacted at 50° C. for 2 hours to graft-polymerize acrylamide at agrafting degree of 173%.

The resulting nonwoven cloth was cut into 10 cm square and dried in adryer at 50° C. for 5 hours. The nonwoven cloth was removed from thedryer and placed on a bench in a room at a relative humidity of 55% anda temperature of 22° C. where it was tested for change with time inweight gain resulting from adsorption of water in the air. A high wateradsorption speed was obtained as shown by weight gains of 4.9% after 3minutes and 8.9% after 10 minutes.

EXAMPLE 4

The strongly acid cation exchange nonwoven cloth prepared in Example 1and a 3 mm mesh diagonal net were layered and rolled up and closelypacked in a glass tube having a diameter of 50 mm. An air flow at arelative humidity of 70% was fed to the glass tube at a flow rate of 50L/min and the effluent air was collected for 5 minutes after inflowstarted. The collected air had a relative humidity of 43%. An air flowat 55° C. was further fed to the glass tube at the same flow rate for 5minutes to desorb water adsorbed to the nonwoven cloth. Then, an airflow at a relative humidity of 70% was fed again at the same flow rateand the effluent air was collected. The collected air had a relativehumidity of 43%, confirming that water adsorbing/desorbing properties ofthe nonwoven material can be repeatedly reproduced.

This composite article of a nonwoven cloth and an oblique net could bevery easily prepared and readily incinerated after use.

COMPARATIVE EXAMPLE 1

A commercially available strongly acid cation exchange resin (DIAXONSK1B from Mitsubishi Chemical) was regenerated with hydrochloric acidand dried. Then, the resin was ground into a powdery ion exchange resinin a mill. This was bonded onto a flame-retardant paper based on ceramicfiber and glass fiber with an adhesive.

This powdery ion exchange resin-bonded paper was cut into 10 cm squareand then dried In a dryer at 60° C. for 3 hours. The powdery ionexchange resin-bonded paper was removed from the dryer and placed on abench in a room at a relative humidity of 70% and a temperature of 25°C. where it was tested for change with time in weight gain resultingfrom adsorption of water in the air. A water adsorption speedcorresponding to weight gains of 3.5% after 3 minutes and 7.1% after 10minutes was obtained. This was inferior to that of the strongly acidcation exchange nonwoven material in Example 1.

The steps of grinding anion exchange resin or bonding the ground ionexchange resin to a flame-retardant paper were laborious and unboundfine powdery ion exchange resin scattered to surroundings. Thisresin-bonded paper was incinerated in anticipation of disposal afteruse, but the ion exchange resin was hard to burn and many other problemsoccurred.

INDUSTRIAL APPLICABILITY

Water adsorbing/desorbing materials of the present inventioncharacterized by having a polymer side chain containing a hydrophilicgroup on the backbone of an organic polymer base have high physicalstrength and rapidly adsorb/desorb and diffuse water molecules, so thatthey can attain more excellent water adsorbing/desorbing performance.Water adsorbing/desorbing materials of the present invention canefficiently desorb water even when the temperature of the regeneratingheating air is low. They can adsorb/desorb not only water but also acidor basic gases and charged particles when an anion exchange group or acation exchange group is introduced as a hydrophilic group. These wateradsorbing/desorbing materials are readily disposable by incineration orother means and lighter and less expensive as compared with conventionalion exchange resins or the like.

The present invention includes the following aspects.

1. A water adsorbing/desorbing material characterized by having apolymer side chain containing a hydrophilic group on the backbone of anorganic polymer base.

2. The water adsorbing/desorbing material as defined in 1 above whereinsaid organic polymer base is in the form of a woven or nonwoven clothconsisting of a fiber assembly.

3. The water adsorbing/desorbing material as defined in 1 or 2 abovewherein said polymer side chain containing a hydrophilic group has beenintroduced onto the backbone of an organic polymer base byradiation-induced graft polymerization.

4. The water adsorbing/desorbing material as defined in any one of 1 to3 above wherein said hydrophilic group is selected from cation exchangegroups, anion exchange groups and non-ion exchange groups.

5. The water adsorbing/desorbing material as defined in 4 above whereinsaid cation exchange group is selected from sulfonate acid group,phosphate group and carboxyl group.

6. The water adsorbing/desorbing material as defined in 4 above whereinsaid anion exchange group is selected from quaternary ammonium group,tertiary amino group, secondary amino group and primary amino group.

7. The water adsorbing/desorbing material as defined in 4 above whereinsaid non-ion exchange group is selected from amide group and hydroxylgroup.

8. A process for preparing the water adsorbing/desorbing material asdefined in any one of 1 to 7 above, comprising graft-polymerizing apolymerizable monomer having a hydrophilic group to an organic polymerbase or graft-polymerizing a polymerizable monomer capable ofintroducing a hydrophilic group and then introducing a hydrophilic grouponto the grafted polymer side chain.

What is claimed is:
 1. A desiccant material for adsorbing/desorbingmoisture in gases, which has a polymer side chain containing ahydrophilic group on the backbone of a polyolefin base, the polymer sidechain being introduced onto the backbone of the polyolefin base byradiation-induced graft polymerization, and wherein the desiccantmaterial has no crosslinked structure.
 2. The desiccant material asdefined in claim 1 wherein said hydrophilic group is a cation exchangegroup selected from sulfonate acid group, phosphate group and carboxylgroup.
 3. The desiccant material as defined in claim 1 wherein saidhydrophilic group is an anion exchange group selected from quaternaryammonium group, tertiary amino group, secondary amino group and primaryamino group.
 4. The desiccant material as defined in claim 1 whereinsaid hydrophilic group is a non-ion exchange group selected from amidegroup and hydroxyl group.
 5. A process for preparing the desiccantmaterial as defined in claim 1, comprising graft-polymerizing apolymerizable monomer having a hydrophilic group to a polyolefin base byradiation-induced graft polymerization or graft-polymerizing apolymerizable monomer capable of introducing a hydrophilic group to apolyolefin base by radiation-induced graft polymerization and thenintroducing a hydrophilic group onto the grafted polymer side chain.